Implantable cardiac devices are used to treat a patient's heart that does not function normally due to, for example, a genetic or acquired condition. A typical implantable cardiac device may perform one or more functions including sensing signals generated in the heart, pacing the heart to maintain regular contractions and providing defibrillation shocks to the heart. Various techniques have been used to implant a cardiac device and associated cardiac leads.
An endocardial implantation technique generally involves gaining access to the interior of the heart via the venous return and implanting one or more leads within the heart. For example, an implantable device including circuitry for sensing signals from and generating stimulation signals for the heart may be subcutaneously implanted in the pectoral region of the patient. Leads connected to the device are routed from the device through a vein to the right side of the heart. A distal end of the lead may then be passively or actively attached to an inner wall of the heart.
An epicardial implantation technique generally involves implanting leads at an outer layer of the heart (e.g., on the epicardium). Advantageously, this technique may enable a physician to place a lead over any of the four chambers of the heart. Traditionally, an implantable device including the sensing and pacing circuitry is implanted in the abdominal region or the pectoral region of the patient. Here, sensing and stimulation leads are routed from the device to the epicardium via an appropriate path.
In addition, some form of fixation mechanism is provided for the epicardial-type lead. For example, a myo-epicardial lead may be fixed in place by screwing a helical electrode into myocardium. An epicardial lead may be fixed in place by suturing or gluing the electrodes onto the epicardial surface. Each of these techniques, however, generally involves an invasive procedure and direct visualization to ensure safety. For example, it is important to avoid damaging any of the arteries on the epicardial surface.